1. Field of the Invention
This invention has to do with removal of urea and/or biuret from a cyanuric acid - inert solvent reaction product, and more particularly from such a reaction product obtained by pyrolytic conversion of urea or biuret in the presence of the inert solvent.
2. Description of the Prior Art
As described in U.S. Pat. No. 3,563,987 and in the art identified therein, it is known that cyanuric acid can be produced by the pyrolysis of urea in an inert solvent, as shown by the equation: ##EQU1## wherein C.sub.3 H.sub.3 O.sub.3 N.sub.3, cyanuric acid (CA, hereinafter), is represented as ##STR1##
Inert solvents which are advantageous for the pyrolysis have a boiling point of at least about 180.degree. C. at pressures up to about 250 mm. of Hg., readily dissolve urea and biuret, have limited solubility for CA, and are not chemically reactive with urea, biuret and CA. Such solvents include alkyl sulfones and cyclic sulfones, such as sulfolane (tetramethylene sulfone).
Residual unpyrolyzed urea/biuret co-precipitates with CA on cooling a sulfolane reaction slurry and contaminates the resulting filter cake, which is subsequently purified. The presence of urea/biuret in a CA cake is undesirable from both a process efficiency and operability standpoint. For maximum sulfolane process efficiency, operability and final CA purity, the levels of urea and biuret in a reactor product cake should be as low as possible (e.g., &gt;1% each). Higher levels than this require greater energy and water consumption in achieving satisfactory CA purification.
It is an object of this invention, therefore, to provide a process to meet the desired urea/biuret impurity levels in a CA reactor cake which is subsequently purified. Such purification is necessary in order to meet accepted product quality specifications and standards.